Electrostatic induction generation device and electrostatic induction generation apparatus having a movable electrode formed between a first fixed electrode substrate and a second fixed electrode substrate

ABSTRACT

An electrostatic induction generation device comprising a first fixed electrode substrate having a first electret electrode, a second fixed electrode substrate having a second electret electrode, a movable electrode substrate having a movable electrode, a holding frame formed separately from the movable electrode, a first pair of electrode support beams and a second pair of electrode support beams connected with the movable electrode and the holding frame, and wherein the movable electrode substrate is formed between the first fixed electrode substrate and the second fixed electrode substrate, and the movable electrode is opposed to the first electret electrode and the second electret electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.13/214,538 filed Aug. 22, 2011 which claims priority to Japanese PatentApplication No. 2010-185854 filed Aug. 23, 2010 all of which areexpressly incorporated by reference herein in their entireties.

BACKGROUND

1. Technical Field

The present invention relates to an electrostatic induction generationdevice and an electrostatic induction generation apparatus.

2. Related Art

In accordance with the recent environmental concerns, electrical powergeneration using natural energy such as electrical power generationusing solar energy or wind energy has been starting to spread widely.However, both of the solar energy and the wind energy must depend on theconditions for installation, namely the environment such that thesunlight is not blocked or that the stable wind is blowing. In contrastthereto, a method of converting the environmental vibration intoelectrical power attracts attention. As such a method, those usingelectromagnetic induction or piezoelectricity can be cited, and inparticular, the electrostatic method using electromagnetic induction isa technology capable of downsizing and cost reduction with a simplestructure.

The principle of the electrical power generation using the electrostaticmethod is as follows. A substrate provided with an electretsemipermanently holding surface electric charge is used as onesubstrate. The other substrate opposed to the one substrate is providedwith an electrode. Then the substrates are moved so as to make arelative movement (displacement) to thereby vary the area of theelectrode opposed to the electret. The variation in the dielectriccharge caused in the electrode is taken out to thereby generateelectricity (Japanese Patent No. 4,338,745 (Document 1)).

In the electrical power generation using the electrostatic method, thecharge held by the electret and the dielectric charge generated on theopposed electrode cause the Coulomb force in the attracting direction toact between electrodes to thereby make the electrodes opposed to eachother with a small gap have contact with each other, which hinders therelative displacement or causes displacement (behavior) in a directiondifferent from the relative displacement direction to thereby make theefficient electrical power generation difficult. Therefore, there hasbeen proposed an electrostatic induction generation provided with aguard and a stopper for limiting the relative displacement (WO08/026,407 brochure (Document 2)).

However, even in the device of Document 2, the contact between the guardand the electrode hinders the normal relative displacement between theelectrodes to thereby make the electrical power generation unstable.

SUMMARY

An advantage of some aspects of the invention is to provide anelectrostatic induction generation device and an electrostatic inductiongeneration apparatus each stabilizing the relative displacement of theelectrodes to thereby efficiently supply the stable electrical power.

Application Example 1

This application example of the invention is directed to anelectrostatic induction generation device including a first fixedelectrode substrate and a second fixed electrode substrate each havingan electret electrode on one surface, and a movable electrode substratehaving at least one movable electrode, a holding frame formed separatelyfrom the movable electrode, and at least one pair of electrode supportbeams adapted to couple two sides of the movable electrode opposed toeach other to the holding frame in a direction perpendicular to amovable direction of the movable electrode, wherein the electretelectrode of the first fixed electrode substrate and the electretelectrode of the second fixed electrode substrate are disposed so as tobe opposed to each other, the movable electrode and the electretelectrode of each of the first fixed electrode substrate and the secondfixed electrode substrate are disposed so as to be opposed to eachother, and the movable electrode substrate is sandwiched between andpartially fixed to the first fixed electrode substrate and the secondfixed electrode substrate.

According to this application example of the invention, since the atleast one pair of electrode support beams disposed in a directionperpendicular to the movable direction of the movable electrode providedto the movable electrode substrate prevents the behavior of the movableelectrode in other directions than the movable direction thereof, theelectrical power generation efficiency is not degraded. Further, sincethe movable electrode substrate is sandwiched by the first fixedelectrode substrate and the second fixed electrode substrate eachprovided with the electret electrode while disposing the electretelectrodes disposed so as to be opposed to each other, the amount ofcharge electrostatically induced in the movable electrode can beincreased, and thus the electricity to be generated can be increased.

Application Example 2

This application example of the invention is directed to theelectrostatic induction generation device of the above applicationexample of the invention, wherein each of the electrode support beamshas a beam length L defined as a distance from a connection point of themovable electrode to a connection point of the holding frame, a beamwidth W in a direction perpendicular to the beam length L in a planview, and a beam thickness T, the beam length L, the beam width W, andthe beam thickness T fulfilling the following relationship.

W/T≦0.1

According to this above application example of the invention, thedisplacement in the direction perpendicular to the vibration directionof the movable electrode can be prevented. Therefore, the highlyefficient electrostatic induction generation device with a smallconversion loss from the vibration applied thereto to the electricitycan be obtained.

Application Example 3

This above application example of the invention is directed to theelectrostatic induction generation device of the above applicationexample of the invention, wherein the movable electrode is formed tohave a plurality of electrode fingers extending in a directionperpendicular to the movable direction of the movable electrode, and anelectrode finger beam connected to both ends of the electrode fingers,each of the electrode support beams extends from the electrode fingerbeam, and the electret electrode of each of the first fixed electrodesubstrate and the second fixed electrode substrate is formed to have aplurality of electret electrode fingers opposed respectively to theplurality of electrode fingers of the movable electrode.

According to this application example of the invention, it becomespossible to increase the amount of the variation in the overlap in aplan view between the electret electrode fingers and the electrodefingers of the movable electrode within the amplitude of the vibrationapplied thereto, and thus the electricity generated can be increased.

Application Example 4

This application example of the invention is directed to theelectrostatic induction generation device of the above applicationexample of the invention, wherein at least two of the movable electrodesare provided, and the at least two movable electrodes are disposed sothat the respective movable directions are perpendicular to each other.

According to this application example of the invention, it is possibleto obtain the electrostatic induction generation device capable ofgenerating electrical power irrespective of the direction of thevibration applied thereto.

Application Example 5

This application example of the invention is directed to anelectrostatic induction generation apparatus using the electrostaticinduction generation device according to the above application exampleof the invention.

According to this application example of the invention, theelectrostatic induction generation apparatus capable of efficientlyconverting the vibration applied from the outside into the electricityto thereby generate electrical power can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is an external perspective view of an electrostatic inductiongeneration device according to a first embodiment of the invention.

FIG. 2 is an external perspective view of the electrostatic inductiongeneration device according to the first embodiment in an explodedstate.

FIG. 3 is a cross-sectional view the A-A′ part of the electrostaticinduction generation device according to the first embodiment shown inFIG. 2.

FIGS. 4A and 4B are cross-sectional views of the electrostatic inductiongeneration device according to the first embodiment, wherein FIG. 4A isa cross-sectional view of the B-B′ part shown in FIG. 2, and FIG. 4Bshows the C-C′ part shown therein.

FIGS. 5A through 5D are diagrams for explaining the electrostaticinduction generation device according to the first embodiment, whereinFIG. 5A is a schematic plan view of a third substrate, FIG. 5B is aconceptual diagram of a cross-section of the D plane shown in FIG. 1,and FIGS. 5C and 5D are enlarged conceptual diagrams of the E partindicated in FIG. 5B for explaining electrostatic induction.

FIGS. 6A through 6C are conceptual diagrams for explaining the operationof electrode support beams of the electrostatic induction generationdevice according to the first embodiment.

FIGS. 7A and 7B are partial enlarged views of the electrode support beamof the electrostatic induction generation device according to the firstembodiment, wherein FIG. 7A is a plan view, and FIG. 7B is across-sectional view of the F-F′ part indicated in FIG. 7A.

FIG. 8 is a schematic perspective view of an electrostatic inductiongeneration device according to a second embodiment of the invention.

FIG. 9 is a block diagram showing an electrostatic induction generationapparatus according to a third embodiment of the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Some embodiments according to the invention will hereinafter beexplained with reference to the accompanying drawings.

First Embodiment

FIG. 1 is an external perspective view showing the electrostaticinduction generation device according to the present embodiment. Theelectrostatic induction generation device 100 shown in FIG. 1 iscomposed of a first substrate 10 as a first fixed electrode substrateprovided with an electret on the fixed electrode described later, amovable substrate 30 provided with a movable section, and a secondsubstrate 20 as a second fixed electrode substrate provided with theelectret on the fixed electrode, stacked so that the first substrate 10and the second substrate 20 sandwich the movable substrate 30.

FIG. 2 is an external perspective view of the electrostatic inductiongeneration device 100 shown in FIG. 1 in an exploded state. The firstsubstrate 10 is a glass substrate, and borosilicate glass, for example,is preferably used therefor. One surface 11 (hereinafter referred to asan electrode forming surface 11) of the first substrate 10 is providedwith a recess 12, and a fixed electrode 13 formed of a metal film madeof, for example, Au, Pt, Ag, Ti or W is formed on a bottom surface 12 aof the recess 12. The fixed electrode 13 includes a plurality of fixedelectrode fingers 13 a extending in the Y direction indicated in thedrawings at predetermined intervals. Further, at least one connectionelectrode 13 b for connecting both or either one of the ends of thefixed electrode fingers 13 a is formed so as to extend in a direction (Xdirection) perpendicular to the fixed electrode fingers 13 a, andfurther, an external connection electrode 13 c formed on the electrodeforming surface 11 and the connection electrode 13 b are connected toeach other.

The first substrate 10 has a roughly rectangular outer shape, and ispartially provided with a notch 10 a. The notch 10 a is for exposing anexternal connection terminal provided to the movable substrate 30described later. The second substrate 20 is formed to have aconfiguration common to the first substrate 10 configured as describedabove, and the constituents identical to the recess 12 and the fixedelectrode 13 formed on the electrode forming surface 11 of the firstsubstrate 10 are provided to the surface opposed to the movablesubstrate 30 although not shown in the drawings.

FIG. 3 is an enlarged cross-sectional view of the first substrate 10shown in FIG. 2 viewed along the A-A′ direction. The fixed electrodefingers 13 a formed on the first substrate 10 are each further providedwith an electret electrode finger 14. The electret electrode finger 14always holds the charge on the surface, and can be formed using a knownmethod. The electret electrode finger 14 is formed on each of the fixedelectrode fingers 13 a extending in the Y direction, and is not providedto a region other than the surface of each of the fixed electrodefingers 13 a. It should be noted that the electret electrode finger 14can also be formed on the connection electrode 13 b extending in the Xdirection perpendicular to the fixed electrode fingers 13 a.

The movable substrate 30 will be explained. The movable substrate 30 isformed of a single-crystal silicon substrate, and the outer shapethereof is formed to have a roughly rectangular shape. A movableelectrode holding frame 31 is formed to have a frame-like shape alongthe outer shape, and an outer shape portion of one side 31 a of themovable electrode holding frame 31 is provided with a notch 30 a formedat a position corresponding to the external connection electrode 13 c ofthe first substrate 10, and a notch 30 b formed at a positioncorresponding to the external connection electrode, not shown, of thesecond substrate 20.

FIG. 4A is a cross-sectional view of the movable substrate 30 along theB-B′ direction indicated in FIG. 2, and FIG. 4B is a cross-sectionalview thereof along the C-C′ direction. Inside the movable electrodeholding frame 31, there is formed a movable electrode 32 having arectangular outer shape separately from the movable electrode holdingframe 31. The movable electrode 32 is provided with a plurality ofmovable electrode fingers 32 a extending in the Y direction shown in thedrawings, and electrode finger beams 32 b coupled to both ends of themovable electrode fingers 32 a and extending in the direction (the Xdirection) perpendicular to the movable electrode fingers 32 a. In thepresent embodiment, the movable electrode 32 vibrates (moves) in thedirection (the X direction) perpendicular to the extending direction ofthe movable electrode fingers 32 a, and the electrical power isgenerated by the variation in the opposed area with respect to theelectret electrode fingers 14 provided to the first substrate 10described above disposed so as to be opposed to the movable electrodefingers 32 a and the electret electrode fingers, not shown, provided tothe second substrate 20. It should be noted that although theexplanation is presented using the plurality of movable electrodefingers 32 a in the above description, it is also possible to adopt theconfiguration of the single movable electrode finger 32 a, namely usingthe flat plate of the movable electrode 32 as the electrode finger.

At least one pair of (two) electrode support beams 33 linking outersides 32 c, 32 d of the movable electrode 32 parallel to the vibrationdirection of the movable electrode 32 respectively to inner sides 31 b,31 c of the movable electrode holding frame 31 opposed to the outersides 32 c, 32 d of the movable electrode 32 are provided to each of theouter sides 32 c, 32 d. In other words, the movable electrode holdingframe 31 holds the movable electrode 32 using the electrode supportbeams 33.

Further, an external connection section 35 is disposed on both or eitherone of the substrate surfaces of the movable substrate 30 at a positioncorresponding to the notch 10 a of the first substrate 10 or the notchof the second substrate 20. The external connection section 35 is ametal film, namely a thin film made of metal such as Au, Pt, Ag, Ti, orW, formed by, for example, an evaporation process or a sputteringprocess, and is used as a connection terminal with a circuit board orthe like.

The first substrate 10, the movable substrate 30, and the secondsubstrate 20 described above are sequentially stacked, and then bondedto each other airtightly via the bonding sections of the respectivesubstrates, namely the movable electrode holding frame 31 of the movablesubstrate 30, and thus the electrostatic induction generation device 100can be obtained. As the bonding process, an anodic bonding process knownto the public, for example, is preferably used. Further, since theinside of the electrostatic induction generation device 100 is sealed invacuo, there is no chance that the motion of the movable electrode 32 ishindered by a gas such as air.

The operation of the electrostatic induction generation device 100according to the present embodiment will be explained. FIGS. 5A through5D are conceptual diagrams for explaining the operation of theelectrostatic induction generation device 100, wherein FIG. 5A is aschematic plan view of the movable substrate 30, FIG. 5B is across-sectional view of the D plane of the electrostatic inductiongeneration device 100 shown in FIG. 1 including the C-C′ cross-sectionof the movable substrate 30, and FIGS. 5C and 5D are enlarged views ofthe E part shown in FIG. 5B.

As shown in FIG. 5A, the electrostatic induction generation device 100according to the present embodiment generates the electrical power usingthe migration of the charge caused by the vibration of the movableelectrode 32 of the movable substrate 30 in the P direction shown in thedrawing. As shown in FIG. 5B, the first substrate 10 and the secondsubstrate 20 are each provided with the fixed electrode fingers 13 a andthe electret electrode fingers 14 formed on the surface of therespective fixed electrode fingers 13 a disposed so as to be opposed tothe respective movable electrode fingers 32 a constituting the movableelectrode 32 of the movable substrate 30. In the resting condition ofthe movable electrode 32 shown in FIG. 5B, the charge is always held onthe surface of the electret electrode fingers 14 as shown in FIG. 5C.Although in the present embodiment, the explanation is presented usingthe example of holding the negative charge on the surface of theelectret electrode fingers 14, the electret holding the positive chargecan also be adopted. On that occasion, the negative charge is induced toand then held by the movable electrode fingers 32 a.

Due to the negative charge e⁻ held on the surface of the electretelectrode fingers 14, the positive charge e⁺ is charged on the surfaceof the movable electrode fingers 32 a of the movable electrode 32 by theelectrostatic induction. In the present condition, if the movableelectrode is displaced in the p direction due to the vibration as shownin FIG. 5D, the overlap M in a plan view between the movable electrodefinger 32 a and the electret electrode finger 14 is reduced, and some ofthe positive charge e⁺ having been held by the movable electrode finger32 a migrates to a power supply device 40 shown in FIG. 5B, namely theelectrical power generation occurs.

Due to the vibration of the movable electrode 32 described above, theelectrical power is generated by repeating the process of taking thepositive charge e+ on the movable electrode finger 32 e by theelectrostatic induction in the condition shown in FIG. 5C, thendisplacing the movable electrode 32 toward the p direction shown in FIG.5D to thereby discharge the charge, returning to the condition of FIG.5C to take the positive charge e+, then moving the movable electrode 32toward the opposite direction to the p direction shown in FIG. 5D in thecondition not shown to thereby discharge the charge, and then returningto the condition shown in FIG. 5C.

In order for vibrating the movable electrode 32 in a stable state, thereare provided the electrode support beams 33 linking the movableelectrode holding frame 31 and the movable electrode 32 to each other.FIGS. 6A through 6C are conceptual diagrams schematically showing themovable substrate 30. The behavior of the electrode support beams 33will be explained with reference to FIGS. 6A through 6C. FIG. 6A showsthe position of the movable electrode 32 in a stopped state. In thisstate, if the vibration is applied to the electrostatic inductiongeneration device 100, and thus the movable electrode 32 is displacedtoward, for example, the arrow p direction shown in FIG. 6B, each of therectangular sections (the hatched sections in the drawings) defined bythe electrode support beams 33, the movable electrode 32, and themovable electrode holding frame is deformed from a rectangular shown inFIG. 6A to a parallelogram shown in FIG. 6B. Further, in the case inwhich the movable electrode 32 is displaced toward the arrow p′direction shown in FIG. 6C, each of the rectangular sections is alsodeformed to a parallelogram. This means that the movable electrode 32 isaccurately translated in the p direction and the p′ direction, namelythe vibration direction perpendicular to the extending direction of themovable electrode fingers 32 a. In other words, the vibration in the pdirection and the p′ direction can accurately be performed, and novibration component in other directions than the p direction and the p′direction is generated.

In the electrostatic induction generation device 100 according to thepresent embodiment, it becomes possible to surely prevent twist of theoverlap in a plane view between the movable electrode fingers 32 a andthe electret electrode fingers 14, the twist being one of the causes ofdegradation in the power generation efficiency and generation ofvariation in the electricity generated, and thus the high-qualityelectrical power generation device can be obtained.

As described above, the electrode support beams 33 are for keeping themovable electrode 32 in the accurate vibration direction, and are set inthe following conditions. FIGS. 7A and 7B are partial enlarged views ofthe electrode support beam 33, wherein FIG. 7A is a plan view, and FIG.7B is a cross-sectional view of the F-F′ part in FIG. 7A. It is assumedthat the beam length of the electrode support beam 33 is L, the beamwidth thereof is W, and the beam thickness thereof is T.

The beam length L is determined based on design values of the resonantfrequency at which the movable electrode 32 resonates with respect tothe environmental vibration (an external vibration) applied to themovable electrode 32, and the amplitude of the vibration of the movableelectrode 32. The beam length L for the movable electrode fingers 32 ais designed based on the displacement amount with which the overlap M inthe plan view can be provided even when the movable electrode 32 isdisplaced due to the vibration as explained with reference to FIG. 5D,namely the amplitude of the vibration at the resonant frequency.

In contrast thereto, the beam width W and the beam thickness T of theelectrode support beam 33 are determined so as to reduce the vibrationcomponent (hereinafter referred to as a movable vertical component) inthe perpendicular direction to the sheet of FIG. 5A showing thevibration direction P, namely in the thickness direction of the movableelectrode 32 as much as possible. Here, the vibration component in thevibration direction P and the movable vertical component can be comparedto each other using the spring constant k_(H) (hereinafter referred toas a horizontal spring constant) of the electrode support beam 33 in thebeam width W direction, and the spring constant k_(V) (hereinafterreferred to as a vertical spring constant) thereof in the beam thicknessT direction.

The horizontal spring constant k_(H) and the vertical spring constantk_(V) are respectively obtained by the following formulas. It should benoted that the following formulas represent the composite springconstant of the four electrode support beams 33 provided to theelectrostatic induction generation device 100 according to the presentembodiment.

$\begin{matrix}{{k_{H} = {E \times T \times \left( \frac{T}{W} \right)^{3}}}{E\text{:}\mspace{14mu} {Young}^{\prime}s\mspace{14mu} {modulus}}} & (1) \\{{k_{V} = {E \times W \times \left( \frac{T}{L} \right)^{3}}}{E\text{:}\mspace{14mu} {Young}^{\prime}s\mspace{14mu} {modulus}}} & (2)\end{matrix}$

According to the formulas 1, 2 described above, k_(V)/k_(H)≦0.01, namelysetting the displacement amount of the movable vertical component withrespect to the displacement amount of the electrode support beam 33 inthe vibration direction P to 1% or lower is preferable. Therefore, it ispreferable to fulfill the relationship of W/T≦0.1.

The beam length L can be obtained by the following formula based on thebeam width W and the beam thickness T thus obtained, and the settingvalues of the resonant frequency and the amplitude of the movableelectrode 32 described above.

$\begin{matrix}{\mspace{20mu} {{{L = \sqrt[3]{\frac{\left( {E \times \alpha^{3} \times T^{4}} \right)}{k}}}\mspace{20mu} {E\text{:}\mspace{14mu} {Young}^{\prime}s\mspace{14mu} {modulus}}\mspace{20mu} {\alpha = \frac{W}{T}}k\text{:}\mspace{14mu} {spring}\mspace{14mu} {constant}\mspace{14mu} {with}\mspace{14mu} {respect}\mspace{14mu} {to}\mspace{14mu} a\mspace{14mu} {vibration}\mspace{14mu} {of}\mspace{14mu} {the}\mspace{14mu} {movable}\mspace{14mu} {electrode}\mspace{14mu} 32}\mspace{20mu} {k = {\left( {2\pi \; f} \right)^{2} \times m}}\mspace{20mu} {f\text{:}\mspace{14mu} {resonant}\mspace{14mu} {frequency}\mspace{14mu} \left( {{natural}\mspace{14mu} {frequency}} \right)}\mspace{20mu} {m\text{:}\mspace{14mu} {mass}\mspace{14mu} {of}\mspace{14mu} {the}\mspace{14mu} {movable}\mspace{14mu} {electrode}}}} & (3)\end{matrix}$

Second Embodiment

A second embodiment of the invention is shown in FIG. 8. Similarly tothe first embodiment, the electrostatic induction generation device 200shown in FIG. 8 is provided with a movable substrate 230, and a firstsubstrate 210 and a second substrate 220 disposed so as to sandwich themovable substrate 230. The movable substrate 230 has a movable electrodeholding frame 231 formed along the outer shape thereof to have a frameshape. A movable electrode 232A and a movable electrode 232B are coupledto the movable electrode holding frame 231 via electrode support beams233 a, 233 b. The extending directions of the movable electrode fingers232 a, 232 b provided to the respective movable electrodes 232A, 232Bare perpendicular to each other. Specifically, in the drawing, themovable electrode fingers 232 a are formed so as to extend in the Ydirection, and the movable electrode fingers 232 b are formed so as toextend in the X direction.

The first substrate 210 used for sandwiching the movable substrate 230is provided with electret electrode fingers 214A, 214B disposed so as toopposed to the movable electrode fingers 232 a of the movable electrode232A provided to the movable substrate 230 and the movable electrodefingers 232 b of the movable electrode 232B provided thereto, and theelectret electrode fingers 214A, 214B are electrically connected to anexternal connection electrode 213 a via a fixed electrode 213.

Similarly, the second substrate 220 is also provided with electretelectrode fingers 224A, 224B disposed so as to opposed to the movableelectrode fingers 232 a of the movable electrode 232A provided to themovable substrate 230 and the movable electrode fingers 232 b of themovable electrode 232B provided thereto, and the electret electrodefingers 224A, 224B are electrically connected to an external connectionelectrode 223 a via a fixed electrode 223.

The first substrate 210, the movable substrate 230, and the secondsubstrate 220 are stacked in the directions shown in FIG. 8 sequentiallyin the order of the first substrate 210, the movable substrate 230, andthe second substrate 220, and then bonded airtightly via the movableelectrode holding frame 231 of the movable substrate 230, and thusformed as the electrostatic induction generation device 200.

Since the electrostatic induction generation device 200 has the movableelectrode fingers 232 a, 232 b extending respectively in the directionsperpendicular to each other as shown in FIG. 8, the electrostaticinduction generation is performed by the movable electrode 232A withrespect to the vibration direction Q shown in the drawing, and theelectrostatic induction generation is performed by the movable electrode232B with respect to the vibration direction R shown in the drawingperpendicular to the vibration direction Q. Therefore, by using theelectrostatic induction generation device 200 according to the presentembodiment, even if the vibration in every direction in the horizontaldirection of the movable substrate 230 is applied, the vibration issplit into the vibration components in the respective vibrationdirections Q, P to thereby make the electrostatic induction generationpossible. Therefore, the electrostatic induction generation device withhigh versatility capable of corresponding to various vibrationdirections can be obtained.

Third Embodiment

As a third embodiment of the invention, an electrostatic inductiongeneration apparatus using the electrostatic induction generation deviceaccording to the first embodiment will be explained. FIG. 9 is a blockdiagram showing the electrostatic induction generation apparatus 1000according to the third embodiment of the invention. The electrostaticinduction generation apparatus 1000 is provided with the electrostaticinduction generation device 100, a power control section 300, and acharging section 400, and supplies the drive device 500 to be a driveobject with the electricity thus generated.

The electricity generated by the electrostatic induction generationdevice 100 is taken out as an irregular current. The power controlsection 300 converts the irregular current into stable electricity, andthen supplies the drive device 500 with the electricity. Further, if thesupply of the electricity to the drive device 500 is not required, thepower control section 300 supplies the charging section 400 with theelectricity to thereby charge a rechargeable device not shown. In orderfor stably supplying the drive device 500 with the electricity, theelectricity thus stored is used in the power control section 300together with the electricity from the electrostatic inductiongeneration device 100 for forming the stable electricity.

The drive device 500 is not particularly limited, but if, for example,an acceleration sensor is used as the drive device 500, theelectrostatic induction generation apparatus according to the presentembodiment can preferably be used as the drive power supply.Specifically, even in the case of installing the sensor in a remoteplace where the power is difficult to get, by providing theelectrostatic induction generation apparatus 1000 resonating with theacceleration (vibration) range to be detected by the accelerationsensor, supply of the drive power to the sensor, power supply to a datatransmitter for transmitting the detection result to a base stationusing wireless communication, and so on are made possible with a simpleapparatus without requiring particular power supply installation work.

Specific Examples

As specific examples, the beam width W, the beam thickness T, and thebeam length L shown in FIGS. 7A and 7B have been compared between thefollowing levels.

Level 1: W=100 μm, T=100 μm

Level 2: W=10 μm, T=100 μm

Level 3: W=5 μm, T=100 μm

Level 4: W=1 μm, T=100 μm

In each of the levels, k_(V)/k_(H) has been obtained as follows.

Level 1: k_(V1)/k_(H1)=1.0

Level 2: k_(V2)/k_(H2)=0.01

Level 3: k_(V3)/k_(H3)=0.0025

Level 4: k_(V4)/k_(H4)=0.0001

Therefore, it has turned up that the level 2 in which the displacementamount of the electrode support beam in the vertical direction withrespect to that in the vibration direction is 1% or lower, namelyW/T=0.1, is preferable. Further, the beam length L=1670 μm has beenobtained.

What is claimed is:
 1. An electrostatic induction generation devicecomprising: a first fixed electrode substrate having a first electretelectrode finger and a second electret electrode finger; a second fixedelectrode substrate having a third electret electrode finger and afourth electret electrode finger; and a movable electrode substratehaving a first electrode finger and a second electrode finger whereinthe movable electrode substrate is formed between the first fixedelectrode substrate and the second fixed electrode substrate, the firstelectrode finger is opposed to the first electret electrode finger andthe third electret electrode finger; the second electrode finger isopposed to the second electret electrode finger and the fourth electretelectrode finger, and the first electrode and the second electrode areformed parallel to each other in a direction perpendicular to a movabledirection of the first electrode and the second electrode.
 2. Theelectrostatic induction generation device according to claim 1, whereinthe movable electrode substrate having a through hole between the firstelectrode finger and the second electrode finger.
 3. The electrostaticinduction generation device according to claim 1, wherein at least twoof the movable electrodes are disposed so that the respective movabledirections are perpendicular to each other.
 4. An electrostaticinduction generation apparatus comprising: the electrostatic inductiongeneration device according to claim
 1. 5. An electrostatic inductiongeneration apparatus comprising: the electrostatic induction generationdevice according to claim 2.